Method and apparatus for operating a vibration isolation system having electronic and pneumatic control systems

ABSTRACT

A method and apparatus for implementing an active vibration isolation system (AVIS) is provided. The AVIS includes a pneumatic control system and an electronic control system. The pneumatic control system supports a mass sensitive to vibration and isolates the mass from high frequency external disturbances. The electronic control system isolates the mass from low frequency external disturbances. The pneumatic control system includes a compliance chamber filled with a fluid to pneumatically support the mass, pressure sensor to measure the pressure level in the compliance chamber, and pneumatic actuator to control the pressure level to minimize the effects of pressure variation in the compliance chamber. The electronic control system includes at least one motion sensor to measure the actual position of the mass as the mass moves due to vibration, at least one feedback system to generate a corresponding signal, an electronic controller to generate signal(s) representing the calculated electronic force needed to compensate for the vibration, and an electronic actuator to generate the electric force to isolate the mass from the external disturbances. The pneumatic and electronic control systems work together to provide high frequency response and eliminate heat dissipation from the electronic control system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vibration isolation apparatus and methods.Particularly, this invention relates to methods and apparatus for anactive vibration isolation system (AVIS) that use a combination ofpneumatic control system and electronic control system to support a massand isolate the mass from external disturbances, such as vibration. TheAVIS may be used in a photolithography process.

2. Description of the Related Art

Photolithography is used for manufacturing integrated circuits. Light istransmitted through non-opaque portions of a pattern on a reticle, orphotomask, through a projection exposure apparatus, and onto a wafer ofspecially-coated silicon or other semiconductor material. The uncoveredportions of the coating that are exposed to light harden. The unhardenedcoating is then removed by an acid bath. Thus, the layer of uncoveredsilicon is altered to produce one layer of the integrated circuit.Conventional systems use visible and ultraviolet light for this process.Recently, however, visible and ultraviolet light have been replaced withelectron, X-ray, and laser beams, which permit smaller feature sizes inthe patterns.

As the miniaturization of a circuit pattern progresses, the focus depthof the projection exposure apparatus becomes very small. As a result, aprimary consideration for an overall design of the photolithographysystem includes building components of the system that achieve precisionby maintaining small tolerances. Any vibration, distortion, ormisalignment caused by external or environmental disturbances must bekept at minimum. These external disturbances affecting an individualpart collectively alter the focusing properties of the photolithographysystem.

Environmental effects may come from, among other things, heat generatedby an electric motor that drives the wafer carrying stage device. Theheat generated from the motor spreads to the surrounding environmentchanging index of refraction of the surrounding gas. In addition, heatalso affects the neighboring components causing the components of thephotolithography system to expand according to their coefficients ofthermal expansion.

Environmental effects may also come from vibrations from moving parts,the ground, or other aspects. Therefore, in a sensitive system wherealignment accuracy is essential, such as a lithography system tomanufacture semiconductor wafers, there is a need for an isolationsystem to substantially reduce vibration.

SUMMARY OF THE INVENTION

The advantages and purposes of the invention will be set forth in partin the description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Theadvantages and purposes of the invention will be realized and attainedby the elements and combinations particularly pointed out in theappended claims.

To attain the advantages and consistent with the principles of theinvention, as embodied and broadly described herein, a first aspect ofthe invention is a method for operating a vibration isolation systemhaving a pneumatic contOorl system and an electronic control system. Themethod comprises the step of generating a pneumatic force in thepneumatic control system to support a mass. The pneumatic force isproduced by a pressure level in a compliance chamber. The pressure levelis being controlled in response to a pressure error signal. The methodalso comprises the steps of delivering the pressure error signal to theelectric control system, and monitoring a motion error signal of themass in the electronic control system. The motion error signal is beingused to generate an electronic force to isolate the mass from vibration.The electronic force is being determined based on a combination of thepressure error signal and the motion error signal.

A second aspect of the present invention is a method for operating avibration isolation system having a pneumatic control system and anelectronic control system. The method comprises the step of monitoring amotion error signal of a mass in the electronic control system. Themotion error signal is being used to generate an electronic errorsignal. The method also comprises the steps of delivering the electronicerror signal to the pneumatic control system, and generating a pneumaticforce in the pneumatic control system to support the mass. The pneumaticforce is being determined based on a combination of the electronic errorsignal and a pressure level in a compliance chamber. The pressure levelis being controlled in response to a pressure error signal. The methodfurther comprises the steps of delivering the pressure error signal tothe electric control system, and generating an electronic force in theelectronic control system to isolate the mass from vibration. Theelectronic force is being determined based on the pressure error signal.

A third aspect of the present invention is a method for operating avibration isolation system having a pneumatic control system and anelectronic control system. the method comprises the steps of generatinga pressure error signal in the pneumatic control system based on apressure signal of a compliance chamber and a reference pressure signal,and controlling the pressure level in the compliance chamber in responseto the pressure error signal, the compliance chamber generating apneumatic force in proportion to the controlled pressure level topneumatically support a mass. The method also comprises the steps ofdelivering the pressure error signal to the electronic control system,comparing a motion signal of the mass in the electronic control systemwith a reference motion signal to generate a motion error signal, andcombining the motion error signal and the pressure error signal. Themethod further comprises the step of determining an electronic force toisolate the mass from vibration based on the combined motion andpressure error signals.

A fourth aspect of the present invention is a method for operating avibration isolation system having a pneumatic control system and anelectronic control system. The method comprises the steps of comparingan actual motion signal of a mass in the electronic control system witha reference motion signal to generate a motion error signal, determiningan electronic error signal based on the motion error signal, anddelivering the electronic error signal to the pneumatic control system.The method also comprises the steps of comparing a pressure signal of acompliance chamber in the pneumatic control system with a referencepressure signal and combining the electronic error signal thereto togenerate a pressure error signal, and controlling the pressure level inthe compliance chamber in response to the pressure error signal. Thecompliance chamber generates a pneumatic force proportionate to thecontrolled pressure level to pneumatically support the mass. The methodfurther comprises the steps of delivering the pressure error signal tothe electronic control system, and determining an electronic force inthe electronic control system based on the pressure error signal toisolate the mass from vibration.

A fifth aspect of the present invention is a vibration isolation system,comprising a pneumatic control system having a compliance chamber togenerate a pneumatic force that supports a mass based on a pressureerror signal, and an electronic control system having a motion sensor togenerate a motion error signal of the mass. The vibration isolationsystem also comprises a force generator connected with the pneumaticcontrol system and the electronic control system. The force generatorgenerates an electronic force based on the results of a combination ofthe pressure error signal and the motion error signal to isolate themass from vibration.

A sixth aspect of the present invention is a vibration isolation systemhaving a pneumatic control system and an electronic control system. Thevibration isolation system comprises a motion sensor, a compliancechamber, a pressure sensor, a pneumatic force generator, and anelectronic force generator. The motion sensor generates a motion errorsignal of a mass in the electronic control system. The motion errorsignal is being used to generate an electronic error signal. Thecompliance chamber and the pressure sensor are provided in the pneumaticcontrol system. The pressure sensor controls a pressure level in thecompliance chamber to generate a pressure error signal. The pneumaticforce generator is connected to the compliance chamber and electroniccontrol system. The pneumatic force generator generates a pneumaticforce that supports the mass based on the results of a combination ofthe electronic error signal and the pressure level in the compliancechamber. The electronic force generator is connected to the pneumaticcontrol system. The electronic force generator generates an electronicforce that isolates the mass from vibration based on the pressure errorsignal.

A seventh aspect of the present invention is a vibration isolationsystem having a pneumatic control system and an electronic controlsystem. The vibration isolation system comprises a pressure sensor and afirst controller. The pressure sensor generates a pressure error signalbased on a pressure information of a compliance chamber and a referencepressure information. The first controller is connected to the pressuresensor for controlling a pressure level in the compliance chamber inresponse to the pressure error signal. The vibration isolation systemalso comprises a pneumatic force generator, a second controller, and anelectronic force generator. The pneumatic force generator is connectedto the first controller for generating a pneumatic force determinedbased on a controlled pressure level to pneumatically support a mass.The second controller is connected to the first controller for comparinga motion information of the mass with a reference motion signal togenerate a motion error signal, and for generating an electronic forcesignal based on the motion error signal and the pressure error signal.The electronic force generator is connected to the second controller forgenerating an electronic force to isolate the mass from vibration basedon the motion error signal and the pressure error signal.

An eighth aspect of the present invention is a vibration isolationsystem having a pneumatic control system and an electronic controlsystem, comprising four controllers. The first controller compares anactual motion signal of a mass in the electronic control system with areference motion signal to generate a motion error signal and todetermine an electronic error signal based on the motion error signal.The second controller compares a pressure signal of a compliance chamberin the pneumatic control system with a reference pressure signal, and tocombine the electronic error signal thereto to generate a pressure errorsignal. The third controller controls the pressure level in thecompliance chamber in response to the pressure error signal. Thecompliance chamber generates a pneumatic force proportionate to thecontrolled pressure level to pneumatically support the mass. The fourthcontroller determines an electronic force in the electronic controlsystem based on the pressure error signal to isolate the mass fromvibration.

A further aspect of the present invention is a vibration isolationsystem using the methods as summarized in the above aspects of theinvention. Yet, a further aspect of the present invention is alithography system comprising the vibration isolation system and anobject on which an image has been formed by the lithography system.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. Additionaladvantages will be set forth in the description which follows, and inpart will be understood from the description, or may be learned bypractice of the invention. The advantages and purposes may be obtainedby means of the combinations set forth in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 is a schematic view of a first embodiment of an active vibrationisolation system (AVIS) consistent with the principles of the presentinvention;

FIG. 2 is a perspective view of a stage device incorporating the AVIS;

FIG. 3 is a schematic view of a first embodiment of the AVIS consistentwith the principles of the present invention in detail;

FIG. 4 is a chart of an electronic force generated by an electronicactuator during a simulation of the AVIS first embodiment;

FIG. 5 is a chart of a pneumatic force generated by pneumatic actuatorduring a simulation of the AVIS first embodiment;

FIG. 6 is a schematic view of a second embodiment of the AVIS consistentwith the principles of the present invention;

FIG. 7 is a chart of an electronic force generated during a simulationof the AVIS second embodiment;

FIG. 8 is an elevation view of an exposure apparatus utilizing an AVIShaving features of the present invention;

FIG. 9 is a flow chart outlining a process for manufacturing anapparatus in accordance with the present invention; and

FIG. 10 is a flow chart outlining an apparatus processing in furtherdetail.

DESCRIPTION OF THE INVENTION

Reference will now be made in detail to several embodiments of methodsand apparatus consistent with the invention, examples of which areillustrated in the accompanying drawings. The invention will be furtherclarified by the following examples, which are intended to be exemplaryof the invention.

A vibration isolation system consistent with the principles of thepresent invention is also referred to as an active vibration isolationsystem (AVIS). The system may be an individual part, a group of parts,or even the system as a whole. For example, in a lithography system, thesystem may be a stage device, a projection exposure apparatus, or anysystem thereof. This invention, however, is not limited to anyparticular application. Rather, the method and system disclosed hereincould be used in any system requiring vibration isolation.

An AVIS 200, illustrated in FIG. 1, includes a pneumatic control system202 and an electric control system 330. Pneumatic control system 202supports a mass 220 and isolates mass 220 from high frequencydisturbances, while electronic control system 330 isolates the mass fromlow frequency disturbances. The electronic control system 330 functionsas the “master” controller, while the pneumatic control system 202 asthe “slave” controller. In this example, mass 220 is a granite base overwhich a wafer stage device 260 moves.

The pneumatic control system 202 includes a compliance chamber 210filled with a fluid to pneumatically support mass 220. Compliancechamber 210 is also shown in FIG. 8 when the AVIS is used to isolatevibration in exposure apparatus 21. The pressure level signal 204 ofcompliance chamber 210 is proportionate to a pneumatic force 276supporting mass 220. Pneumatic control system 202 also includes apressure sensor 212 for measuring the pressure level in the compliancechamber. Pneumatic control system 202 further includes a pneumaticfeedback system 214 and a pneumatic actuator 280 (shown in FIGS. 3 and6) for controlling the pressure level in compliance chamber 210 tomaintain a constant pressure level therein. FIG. 1 illustrates pneumaticactuator 280 as a combination of a fluid supply 222 connected to asupply regulator 224, and a bellows 230 connected to an actuator 232.The supply regulator 224 and actuator 232 control the pressure level incompliance chamber 210 by controlling the fluid flow between compliancechamber 210 and fluid supply 222 and bellows 230, respectively.

Pneumatic control device 202 also includes a pneumatic feedforwardsystem 240, such as a computer, which determines a reference pressuresignal 228 of compliance chamber 210 based on low frequency signal 206.Low frequency signal 206 is based on the weight of mass 220 and theposition of a center of gravity of mass 220. Reference pressure signal228 represents the pressure level necessary to maintain the constantposition of mass 220. Pneumatic control device 202 also includes asumming junction 242 to calculate a difference between referencepressure signal 228 and measured pressure signal 226 and to generate apressure error signal 244. In response to pressure error signal 244,pneumatic actuator 280 controls the pressure level in compliance chamber210 so that pressure level signal 204 is substantially equal toreference signal 228.

Electronic control system 330 includes a position sensor 352, a positionfeedback system 360, and an electronic actuator 350. Position sensor 352and electronic actuator 350 are also shown in FIG. 8 when the AVIS isused to isolate vibration in exposure apparatus 21. Position sensor 352detects a position 356 of mass 220 with respect to a reference point,for example, the ground 82, as mass 220 vibrates or moves due toexternal disturbances. Position feedback system 360, upon receiving theactual position 356, generates a position signal 364.

In addition, electronic control system 330 may also include a velocitysensor 354 (see also FIG. 8) and velocity feedback system 362. Velocitysensor 354 measures an actual velocity 358 of mass 220 caused by theexternal disturbances. Velocity feedback system 362, upon receiving theactual velocity 358, generates a velocity signal 366.

Further, electronic control system 330 includes an electronicfeedforward system 372, which uses a computerized mathematical model ofthe AVIS 200 to generate a disturbance canceling force signal 368representing a force to be exerted on mass 220 to compensate for knowndisturbances.

Position signal 364, velocity signal 366, and disturbance cancelingforce signal 368 enter a summing junction 374, which calculates anelectronic error signal 370 and delivers it to electronic actuator 350.Electronic actuator 350 then exerts an electronic force 376corresponding to electronic error signal 370 onto mass 220 to compensatefor a positional drift of mass 220 with respect to reference point 82and for vibration caused by disturbances.

In one embodiment, as illustrated in FIG. 2, a stage device 100 issupported and isolated from vibration by implementing a plurality of(commonly at least three) AVIS 200, such as is shown in FIG. 1. Stagedevice 100 includes AVIS 200 a and 200 b, each including pneumaticcontrol system 202 a and 202 b, respectively, and electronic controlsystem 330 a and 330 b, respectively, to generate force supporting stagedevice 100 and counteracting vibration parallel to z-axis. A third AVIS(not shown) is located on an edge of stage device 100 opposite from AVIS200 a, 200 b, and generally coinciding with positive y-axis. Stagedevice 100 also includes at least one electronic control system 150 togenerate force counteracting vibration parallel to y-axis. Finally,stage device 100 preferably includes at least one electronic controlsystem 152 to generate force counteracting vibration parallel to x-axis.Stage device 100 is also illustrated having a series of position sensors352 a, 352 b, 352 c, and velocity sensors 354 a, 354 b, 354 c.

According to the conventional AVIS, the pneumatic control system cangenerate a large pneumatic force to support the mass without generatingheat, but it does not have a high frequency response. And, although theelectronic control system has a high frequency response, it generatesheat and consumes a lot of power to generate a large electronic force tosupport the mass. Another disadvantage of the conventional AVIS is thatthe pneumatic and electronic control systems work independent of eachother. In addition, the response time for pneumatic control system tothe generate pneumatic force is high due to the natural frequency of apneumatic system. Consequently, the electronic control system mustgenerate the electronic force to compensate for the late response ofpneumatic control system. When the electronic control system generatesthe electronic force, heat is also inevitably generated. As discussed inthe Description of the Related Art, the heat generated subsequentlyalters the thermal properties of surrounding air and lithography partswhich subsequently reduces the focus precision of the lithographysystem.

Subsequently, the following describes an AVIS control system and methodhaving pneumatic and electronic control systems that can maximize theindividual output thereof, to provide high frequency vibration control,eliminate the heat dissipation, and prevent the electronic and pneumaticactuators from working against each other.

Consistent with the principles of the present invention as illustratedin FIGS. 1, 3, and 8. AVIS also includes a pneumatic control system 202and an electronic control system 330. FIG. 8 illustrates when the AVISis used to isolate vibration in exposure apparatus

Electronic control system 330 has at least one motion sensor, at leastone feedback system, an electronic actuator 350, and a feedforwardsystem.

Consistent with the principles of the invention, a method and apparatusfor maximizing operation of an active vibration isolation system will bedescribed. In the pneumatic control system 202, pressure sensor 212measures the pressure level 204 of compliance chamber 210. Pneumaticfeedback system 214 determines a measured pressure signal 226 based onthe measured pressure level 204, and delivers the measured pressuresignal 226 to summing junction 242.

Summing junction 242 combines measured pressure signal 226, assigned ashaving a negative value, and reference pressure signal 228, having apositive value, to generate a pressure error signal 244. Pressure errorsignal 244 is then used by pneumatic control system 202 and electroniccontrol system 330.

As shown in FIG. 3, motion sensors of electronic control system 330include a position sensor 352 and a velocity sensor 354, shown as asingle element for convenience. Position sensor 352 measures a positionof mass 220 relative to a reference point, such as ground, and generatesa position signal 364. Position signal 364 is delivered to summingjunction 374. Velocity sensor 354 measures an absolute velocityrepresenting vibration of mass 220 caused by the external disturbances,and generates a velocity signal 366. Velocity signal 366 is delivered tosumming junction 374.

In alternative embodiments, only one of position sensor 352 and velocitysensor 354 is used. When both position sensor 352 and velocity sensor354 are used, however, summing junction 374 compares the sum of positionsignal 364 and velocity signal 366 with a reference motion signal 342that includes a reference position signal and a reference velocitysignal. The sum of position signal 364 and velocity signal 366 is anegative value input to summing junction 374, whereas reference motionsignal 342 is a positive value input. Reference motion signal 342including a reference position signal (not shown) and a referencevelocity signal (also not shown). Reference motion signal 342 isdetermined by first motion controller 340, such as a computer simulatinga mathematical model of the AVIS 200. Summing junction 374 generates amotion error signal 375 in response to the signals.

Based on motion error signal 375, a second motion controller 377determines a motion force error signal 379 representing the force neededto cancel positional drift of mass 220 as detected by position sensor352 and vibration of mass 220 as detected by velocity sensor 354. Secondmotion controller 377 may be any device capable of computing motionforce error signal 379. In one embodiment, second motion controller 377is a programmable computer implementing a mathematical calculation in aloop control filter.

Electronic control system 330 also includes an electronic feedforwardsystem 372 to generate a disturbance canceling force signal 368. In oneembodiment, electronic feedforward system 372 is a computer thatsimulates a mathematical model based on the weight and position of thecenter of gravity of mass 220 to determine disturbance canceling forcesignal 368, which compensates for other disturbances not detected byposition sensor 352 nor velocity sensor 354.

Summing junction 384 combines motion force error signal 379 anddisturbance canceling force signal 368 to generate an electronic errorsignal 370.

Consistent with the principles of the present invention, pressure errorsignal 244 from the pneumatic control system 202 is fed forward toelectronic control system 330. The response time for pneumatic controlsystem 202 is relatively low compared with electronic control system330. By feeding pressure error signal 244 to electronic control system330, AVIS 200 utilizes the fast response of electronic actuator 350 tomaximize system bandwidth, encompassing a broad range of operatingfrequency of AVIS 200.

Summing junction 381 sums pressure error signal 244 and electronic errorsignal 370, and delivers the sum to an electronic actuator 350.Electronic actuator 350, for example a motor, converts this sum intoelectronic force 376. Electronic force 376 represents the physical forcethat electronic control system 330 generates to support and isolate mass220. Electronic force 376 and pneumatic force 276 collectively exert atotal force 383 on mass 220 to support and isolate mass 220 fromvibration.

FIGS. 4 and 5 show the results of a simulation of the AVIS 200 accordingto the first embodiment. FIG. 4 represents electronic force 376 inNewtons along the y-axis over a period of time in seconds along thex-axis. FIG. 5 represents pneumatic force 276 in Newtons along they-axis over a period of time in seconds along the x-axis. The sum ofpneumatic force 276 and electronic force 376 represents total force 383,which should be a constant value to isolate mass 220 from the externaldisturbances.

The first embodiment reduces the lagging response time of pneumaticcontrol system 202 by feedforwarding pressure error signal 244 to theelectronic control system 330. Therefore, the overall errors as measuredby pressure sensor 212, position sensor 352, and velocity sensor 354 aresimultaneously corrected. The AVIS 200 according to the first embodimentmay still, however, generate excessive heat for a heat sensitive system,such as a lithography system, because the electronic control system 330is used to compensate for the error due to the slow response ofpneumatic control system 202. Upon receiving the pressure error signal244, the electronic control system 330 generates electronic force 376 tooffset the lagging of pneumatic control system 202, i.e., a DC force of−20 Newtons. This DC force generates the problematic heat.

A second embodiment of the present invention, illustrated in FIG. 6, isdirected to a method and apparatus for maximizing operation of the AVISwhich reduces the response time of the pneumatic control system, andeliminates or substantially reduces the heat problem. Consistent withthe principles of the invention, a method and apparatus are provided tomaximize operation of an active vibration isolation system.

Similar to the first embodiment, in pneumatic control system 202,pressure sensor 212 measures pressure level 204 of compliance chamber210. Pressure sensor 212 measures pressure level 204 to generate ameasured pressure signal 226, which is then delivered to summingjunction 242.

Summing junction 242 compares measured pressure signal 226 of compliancechamber 210 with a reference pressure signal 228. Pneumatic feedforwardsystem 240, such as a computer, may be used to calculate referencepressure signal 228, which is delivered to summing junction 242.

According to the second embodiment, electronic error signal 370 fromelectronic control system 330 is delivered to summing junction 242 ofpneumatic control system 202. Summing junction 242 sums electronic errorsignal 370 as a positive value, measured pressure signal 226 as anegative value, and reference pressure signal 228 as a positive value,to generate a pressure error signal 244. The pressure error signal 244is then, similar to the first embodiment, used for both pneumaticcontrol system 202 and electronic control system 330.

In pneumatic control system 202, in response to pressure error signal244, the pneumatic actuator 280 controls the pressure level incompliance chamber 210 to maintain constant pressure level 204.Compliance chamber 210 generates a pneumatic force 276 in proportion tothe pressure level 204 to support mass 220.

Electronic control system 330, similar to the first embodiment, includesmotion sensors such as a position sensor 352 and a velocity sensor 354,shown as a single element for convenience. Position sensor 352 measuresa position of mass 220 relative to a reference point, such as ground,and generates a position signal 364. Position signal 364 is delivered tosumming junction 374. Velocity sensor 354 measures an absolute velocityrepresenting vibration of mass 220 caused by external disturbances, andgenerates a velocity signal 366. Velocity signal 366 is delivered tosumming junction 374.

In alternative embodiments, only one of position sensor 352 and velocitysensor 354 is used. When both position sensor 352 and velocity sensor354 are used, however, summing junction 374 compares the sum of positionsignal 364 and velocity signal 366 with a reference motion signal 342.The sum of position signal 364 and velocity signal 366 is a negativevalue input to summing junction 374, whereas reference motion signal 342is a positive value input. Reference motion signal 342 is determined byfirst motion controller 340, such as a computer simulating amathematical model of AVIS 200. Summing junction 374 generates a motionerror signal 375 in response to the signals.

Based on motion error signal 375, a second motion controller 377determines a motion force error signal 379 representing the force neededto cancel positional drift of mass 220 as detected by position sensor352 and vibration of mass 220 as detected by velocity sensor 354. Secondmotion controller 377 may be any device capable of computing motionforce error signal 379. In one embodiment, second motion controller 377is a programmable computer implementing a mathematical calculation in acontrol loop filter.

Also similar to the first embodiment, electronic control system 330includes an electronic feedforward system 372 to generate a disturbancecanceling force signal 368. In one embodiment, electronic feedforwardsystem 372 is a computer that simulates a mathematical model based onthe weight and position of the center of gravity of mass 220 todetermine disturbance canceling force signal 368, which compensates forother disturbances not detected by position sensor 352 nor velocitysensor 354.

Summing junction 384 combines motion force error signal 379 anddisturbance canceling force signal 368 to generate an electronic errorsignal 370.

Unlike the first embodiment, electronic error signal 370 is then fedforward to summing junction 242 of the pneumatic control system 202.Therefore, according to the second embodiment, summing junction 242combines measured pressure signal 226 as a negative value, referencepressure signal 228 as a position value, and electronic error signal 370as a positive value, to generate pressure error signal 244.

Similar to the first embodiment, pressure error signal 244 is used forboth pneumatic 202 and electronic 330 control system. According to thesecond embodiment, however, pneumatic control system 202 is utilized tocorrect pressure, positional, and velocity errors, as well as othererrors not detected by sensors 212, 352, 354, because pressure errorsignal 244 includes electronic error signal 370. Therefore, electricforce 376 generated by electric actuator 350 is reduced, therebyreducing the heat associated therewith.

According to the second embodiment, in the electronic control system330, pressure error signal 244 is also fed forward to electronicactuator 350. Therefore, electronic control system 330 utilizes the fastresponse of electronic actuator 350 to compensate for the balance ofpressure, positional, and velocity errors that pneumatic control system202 is too slow to correct. Electronic actuator 350 converts pressureerror signal 244 into an electronic force 376. The electronic force 376and pneumatic force 276 collectively exert total force 383 to supportmass 220 and isolate it from vibration.

FIG. 7 shows of a simulation of the AVIS 200 according to the secondembodiment under conditions similar to the first embodiment. FIG. 7represents electronic force 376 in Newtons along the y-axis over aperiod of time in seconds along the x-axis. Electronic force 376 levelsoff at 0 Newtons after passing a short period of time. Therefore,electronic control system 330 generates little, if any, DC force tocompensate a steady state error of pneumatic reference signal 228, thus,overcoming the heat problem.

AVIS 200 is particularly useful to isolate stage device(s) of anexposure apparatus in a lithography process. In operation, exposureapparatus 21 shown in FIG. 8 transfers a pattern of an integratedcircuit from reticle 80 onto semiconductor wafer 68. Exposure apparatus21 mounts to a base 82, i.e., a floor or the ground or some othersupporting structure, or is supported by an AVIS.

Apparatus frame 72 is rigid and supports the components of the exposureapparatus 21. The design of the apparatus frame 72 can be varied to suitthe design requirements for the rest of exposure apparatus 21. Apparatusframe 72 illustrated in FIG. 8, supports reticle stage 76, lens assembly78, and illumination system 74 above base 64. Wafer stage 66 issupported by AVIS 200 individually from apparatus frame 72. Alternately,for example, an integrated structure (not shown) can be used to ifsupport wafer stage 66 and reticle stage 76, illumination system 74, andlens assembly 78 above base 82.

Illumination system 74 includes an illumination source 84 and anillumination optical assembly 86. Illumination source 84 emits the beam(irradiation) of light energy. Illumination optical assembly 86 guidesthe beam of light energy from illumination source 84 to lens assembly78. The beam illuminates selectively different portions of reticle 80and exposes wafer 68. In FIG. 8, illumination source 84 is illustratedas being supported above reticle stage 76. Typically, however,illumination source 84 is secured to one of the sides of apparatus frame72 and the energy beam from illumination source 84 is directed to abovereticle stage 76 with illumination optical assembly 86.

Lens assembly 78 projects and/or focuses the light passing throughreticle 80 to wafer 68. Depending upon the design of apparatus 21, lensassembly 78 can magnify or reduce the image illuminated on reticle 80.

Wafer stage 66 and/or reticle stage 76 are isolated from vibration byAVIS 200 (not shown) consistent with the principles of the presentinvention. Reticle stage 76 holds and precisely positions reticle 80.relative to lens assembly 78 and wafer 68. Somewhat similarly, waferstage 66 holds and positions wafer 68 with respect to the projectedimage of the illuminated portions of reticle 80. In the embodimentillustrated in FIG. 8, wafer stage 66 and reticle stage 76 arepositioned by a plurality of motors 10. Depending upon the design,apparatus 21 can also include additional servo drive units, linearmotors and planar motors to move wafer stage 66 and reticle stage 76.

There are a number of different types of photolithographic devices. Forexample, exposure apparatus 21 can be used as a scanning typephotolithography system which exposes the pattern from reticle 80 ontowafer 68 with reticle 80 and wafer 68 moving synchronously. In ascanning type lithographic device, reticle 80 is moved perpendicular toan optical axis of lens assembly 78 by reticle stage 76 and wafer 68 ismoved perpendicular to an optical axis of lens assembly 78 by waferstage 66. Scanning of reticle 80 and wafer 68 occurs while reticle 80and wafer 68 are moving synchronously.

Alternately, exposure apparatus 21 can be a step-and-repeat typephotolithography system that exposes reticle 80 while reticle 80 andwafer 68 are stationary. In the step and repeat process, wafer 68 is ina constant position relative to reticle 80 and lens assembly 78 duringthe exposure of an individual field. Subsequently, between consecutiveexposure steps, wafer 68 is consecutively moved by wafer stage 66perpendicular to the optical axis of lens assembly 78 so that the nextfield of semiconductor wafer 68 is brought into position relative tolens assembly 78 and reticle 80 for exposure. Following this process,the images on reticle 80 are if sequentially exposed onto the fields ofwafer 68.

However, the use of exposure apparatus 21 provided herein is not limitedto a photolithography system for semiconductor manufacturing. Exposureapparatus 21, for example, can be used as an LCD photolithography systemthat exposes a liquid crystal display device pattern onto a rectangularglass plate or a photolithography system for manufacturing a thin filmmagnetic head. Further, the present invention can also be applied to aproximity photolithography system that exposes a mask pattern by closelylocating a mask and a substrate without the use of a lens assembly.Additionally, the present invention provided herein can be used in otherdevices, including other semiconductor processing equipment, machinetools, metal cutting machines and, inspection machines.

The illumination source 84 can be g-line (436 nm), i-line (365 nm), KrFexcimer laser (248 nm), ArF excimer laser (193 nm) and F₂ laser (157nm). Alternately, illumination source 84 can also use charged particlebeams such as x-ray and electron beam. For instance, in the case wherean electron beam is used, thermionic emission type lanthanum hexaboride(LaB₆) or tantalum (Ta) can be used as an electron gun. Furthermore, inthe case where an electron beam is used, the structure could be suchthat either a mask is used or a pattern can be directly formed on asubstrate without the use of a mask.

In terms of the magnification of lens assembly 78 included in thephotolithography system, lens assembly 78 need not be limited to areduction system. It could also be a 1x or magnification system.

With respect to lens assembly 78, when far ultra-violet rays such as theexcimer laser is used, glass materials such as quartz and fluorite thattransmit far ultra-violet rays is preferable to be used. When the F₂type laser or x-ray is used, lens assembly 78 should preferably beeither catadioptric or refractive (a reticle should also preferably be areflective type), and when an electron beam is used, electron opticsshould preferably comprise electron lenses and deflectors. The opticalpath for the electron beams should be in a vacuum.

Also, with an exposure device that employs vacuum ultra-violet radiation(VUV) of wavelength 200 nm or lower, use of the catadioptric typeoptical system can be considered. Examples of the catadioptric type ofoptical system include the disclosure Japan Patent ApplicationDisclosure No. 8-171054 published in the Official Gazette for Laid-OpenPatent Applications and its counterpart U.S. Pat. No, 5,668,672, as wellas Japan Patent Application Disclosure No. 10-20195 and its counterpartU.S. Pat. No. 5,835,275. In these cases, the reflecting optical devicecan be a catadioptric optical system incorporating a beam splitter andconcave mirror. Japan Patent Application Disclosure No. 8-334695published in the Official Gazette for Laid-Open Patent Applications andits counterpart U.S. Pat. No. 5,689,377 as wall as Japan PatentApplication Disclosure No. 10-3039 and its counterpart U.S. patentapplication Ser. No. 873,606 (Application Date: Jun. 12, 1997) also usea reflecting-refracting type of optical system incorporating a concavemirror, etc., but without a beam splitter, and can also be employed withthis invention. As far as is permitted, the disclosures in theabovementioned U.S. patents, as well as the Japan patent applicationspublished in the Official Gazette for Laid-Open Patent Applications areincorporated herein by reference.

Further, in photolithography systems, when linear motors (see U.S. Pat.Nos. 6,623,853 or 5,528,118) are used in a wafer stage or a mask stage,the linear motors can be either an air levitation type employing airbearings or a magnetic levitation type using Lorentz force or reactanceforce. Additionally, the stage could move along a guide, or it could bea guideless type stage which uses no guide. As far as is permitted, thedisclosures in U.S. Pat. Nos. 5,623,853 and 5,528,118 are incorporatedherein by reference.

Alternatively, one of the stages could be driven by a planar motor,which drives the stage by electromagnetic force generated by a magnetunit having two-dimensionally arranged magnets and an armature coil unithaving two-dimensionally arranged coils in facing positions. With thistype of driving system, either one of the magnet unit or the armaturecoil unit is connected to the stage and the other unit is mounted on themoving plane side of the stage.

Movement of the stages as described above generates reaction forceswhich can affect performance of the photolithography system. Reactionforces generated by the wafer (substrate) stage motion can bemechanically released to the floor (ground) by use of a frame member asdescribed in U.S. Pat. No. 5,528,118 and published Japanese PatentApplication Disclosure No. 8-166475. Additionally, reaction forcesgenerated by the reticle (mask) stage motion can be mechanicallyreleased to the floor (ground) by use of a frame member as described inU.S. Pat. No. 5,874,820 and published Japanese Patent ApplicationDisclosure No. 8-330224. As far as is permitted, the disclosures in U.S.Pat. Nos. 5,528,118 and 5,874,820 and Japanese Patent ApplicationDisclosure No. 8-330224 are incorporated herein by reference.

As described above, a photolithography system according to the abovedescribed embodiments can be built by assembling various subsystems,including each element listed in the appended claims, in such a mannerthat prescribed mechanical accuracy, electrical accuracy and opticalaccuracy are maintained. In order to maintain the various accuracies,prior to and following assembly, every optical system is adjusted toachieve its optical accuracy. Similarly, every mechanical system andevery electrical system are adjusted to achieve their respectivemechanical and electrical accuracies. The process of assembling eachsubsystem into a photolithography system includes mechanical interfaces,electrical circuit wiring connections and air pressure plumbingconnections between each subsystem. Needless to say, there is also aprocess where each subsystem is assembled prior to assembling aphotolithography system from the various subsystems. Once aphotolithography system is assembled using the various subsystems, totaladjustment is performed to make sure that every accuracy is maintainedin the complete photolithography system. Additionally, it is desirableto manufacture an exposure system in a clean room where the temperatureand purity are controlled.

Further, semiconductor devices can be fabricated using the abovedescribed systems, by the process shown generally in FIG. 9. In step 301the device's function and performance characteristics are designed.Next, in step 302, a mask (reticle) having a pattern is designedaccording to the previous designing step, and in a parallel step 303, awafer is made from a silicon material. The mask pattern designed in step302 is exposed onto the wafer from step 303 in step 304 by aphotolithography system described hereinabove consistent with theprinciples of the present invention. In step 306 the semiconductordevice is assembled (including the dicing process, bonding process andpackaging process), then finally the device is inspected in step 306.

FIG. 10 illustrates a detailed flowchart example of the above-mentionedstep 304 in the case of fabricating semiconductor devices. In step 311(oxidation step), the wafer surface is oxidized. In step 312 (CVD step),an insulation film is formed on the wafer surface. In step 313(electrode formation step), electrodes are formed on the wafer by vapordeposition. In step 314 (ion implantation step), ions are implanted Inthe wafer. The above mentioned steps 311-314 form the preprocessingsteps for wafers during wafer processing, and selection is made at eachstep according to processing requirements.

At each stage of wafer processing, when the above-mentionedpreprocessing steps have been completed, the following post-processingsteps are implemented. During post-processing, initially, in step 315(photoresist formation step), photoresist is applied to a wafer. Next,in step 316, (exposure step), the above-mentioned exposure device isused to transfer the circuit pattern of a mask (reticle) to a wafer.Then, in step 317 (developing step), the exposed wafer is developed, andin step 318 (etching step), parts other than residual photoresist(exposed material surface) are removed by etching. In step 319(photoresist removal step), unnecessary photoresist remaining afteretching is removed.

Multiple circuit patterns are formed by repetition of thesepreprocessing and post-processing steps.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the methods described, instage device, the material chosen for the present invention, and inconstruction of the photolithography systems as well as other aspects ofthe invention without departing from the scope or spirit of theinvention.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims and theirequivalents.

We claim:
 1. A method for operating a vibration isolation system havinga pneumatic control system and an electronic control system, comprisingthe steps of: monitoring a motion error signal of a mass in theelectronic control system, the motion error signal being used togenerate an electronic error signal; delivering the electronic errorsignal to the pneumatic control system; generating a pneumatic force inthe pneumatic control system to support the mass, the pneumatic forcebeing determined based on a combination of the electronic error signaland a pressure level in a compliance chamber, the pressure level beingcontrolled in response to a pressure error signal; delivering thepressure error signal to the electric control system; and generating anelectronic force in the electronic control system to isolate the massfrom vibration, the electronic force being determined based on thepressure error signal.
 2. The method of claim 1, wherein the step ofmonitoring a motion error signal in the electronic control system,further comprises: measuring a motion of the mass to generate a motionsignal; and generating the motion error signal based on the motionsignal and a reference motion signal.
 3. The method of claim 2, whereinthe step of measuring a motion, further comprises: measuring a positionof the mass.
 4. The method of claim 3, wherein the step of generatingthe motion error signal, further comprises: determining a positionsignal based on the measured position; and comparing the position signalwith a reference position signal to generate the motion error signal. 5.The method of claim 2, wherein the step of measuring a motion, furthercomprises: measuring a velocity of the mass.
 6. The method of claim 5,wherein the step of generating the motion error signal, furthercomprises: determining a velocity signal based on the measured velocity;and comparing the velocity signal with a reference velocity signal togenerate the motion error signal.
 7. The method of claim 3, furthercomprising: determining the reference motion signal.
 8. The method ofclaim 7, further comprising: determining a motion force error signalbased on the motion error signal.
 9. The method of claim 8, furthercomprising: generating a disturbance canceling force signal tocounteract the motion force error signal, and resulting in an electronicerror signal.
 10. The method of claim 9, wherein the step of generatinga disturbance canceling force signal, further comprises: determining thedisturbance canceling force signal.
 11. The method of claim 1, whereinthe step of generating a pneumatic force in the pneumatic controlsystem, further comprises: measuring the pressure level of thecompliance chamber; and determining a pressure signal based on themeasured pressure level.
 12. The method of claim 1, wherein the step ofgenerating a pneumatic force, further comprises: comparing the pressuresignal with a reference pressure signal, and combining the electronicerror signal thereto to generate a pressure error signal.
 13. The methodof claim 12, wherein the step of generating a pneumatic force, furthercomprises. controlling the pressure level in the compliance chamber inresponse to the pressure error signal.
 14. The method of claim 12,wherein the step of generating a pneumatic force, further comprises:determining the reference pressure signal.
 15. The method of claim 1,wherein the step of generating a pneumatic force in the pneumaticcontrol system, further comprises: maintaining a constant pressure levelin the compliance chamber.
 16. The method of claim 1, wherein the stepof generating an electronic force in the electronic control system,further comprises: determining the electronic force based on thepressure error signal.
 17. A method for operating a vibration isolationsystem having a pneumatic control system and an electronic controlsystem, comprising the steps of: comparing an actual motion signal of amass in the electronic control system with a reference motion signal togenerate a motion error signal; determining an electronic error signalbased on the motion error signal; delivering the electronic error signalto the pneumatic control system; comparing a pressure signal of acompliance chamber in the pneumatic control system with a referencepressure signal, and combining the electronic error signal thereto togenerate a pressure error signal; controlling the pressure level in thecompliance chamber in response to the pressure error signal, thecompliance chamber generating a pneumatic force proportionate to thecontrolled pressure level to pneumatically support the mass; deliveringthe pressure error signal to the electronic control system; determiningan electronic force in the electronic control system based on thepressure error signal to isolate the mass from vibration.
 18. The methodof claim 17, wherein the step of comparing an actual motion signal inthe electronic control system, further comprises: measuring a positionof the mass; determining a position signal based on the measuredposition; and comparing the position signal with a reference positionsignal to generate the motion error signal.
 19. The method of claim 17,wherein the step of comparing an actual motion signal in the electroniccontrol system, further comprises: measuring a velocity of the mass;determining a velocity signal based on the measured velocity; andcomparing the velocity signal with a reference velocity signal togenerate the motion error signal.
 20. The method of claim 17, whereinthe step of determining an electronic error signal in the electroniccontrol system, further comprising: determining a motion force errorsignal based on the motion error signal.
 21. The method of claim 20,wherein the step of determining an electronic error signal in theelectronic control system, further comprising: generating a disturbancecanceling force signal to counteract the motion force error signal, andresulting in the electronic error signal.
 22. The method of claim 17,wherein the step of comparing a measured pressure signal in thepneumatic control system, further comprises: measuring the pressurelevel in the compliance chamber to generate a pressure signal; anddetermining the pressure signal based on the measured pressure level.23. The method of claim 17, wherein the step of controlling the pressurelevel in the pneumatic control system, further comprises: maintaining aconstant pressure level in the compliance chamber.
 24. A vibrationisolation system having a pneumatic control system and an electroniccontrol system, comprising: a motion sensor to generate a motion errorsignal of a mass in the electronic control system, the motion errorsignal being used to generate an electronic error signal; a compliancechamber and a pressure sensor in the pneumatic control system, thepressure sensor controlling a pressure level in the compliance chamberto generate a pressure error signal; a pneumatic force generatorconnected to the compliance chamber and electronic control system, thepneumatic force generator generating a pneumatic force that supports themass based on the results of a combination of the electronic errorsignal and the pressure level in the compliance chamber; an electronicforce generator connected to the pneumatic control system, theelectronic force generator generating an electronic force that isolatesthe mass from vibration based on the pressure error signal.
 25. Avibration isolation system having a pneumatic control system and anelectronic control system, comprising: a first controller to compare anactual motion signal of a mass in the electronic control system with areference motion signal to generate a motion error signal, and todetermine an electronic error signal based on the motion error signal; asecond controller to compare a pressure signal of a compliance chamberin the pneumatic control system with a reference pressure signal, and tocombine the electronic error signal thereto to generate a pressure errorsignal; a third controller to control the pressure level in thecompliance chamber in response to the pressure error signal, thecompliance chamber generating a pneumatic force proportionate to thecontrolled pressure level to pneumatically support the mass; a fourthcontroller to determine an electronic force in the electronic controlsystem based on the pressure error signal to isolate the mass fromvibration.